| Wind power industry has developed significantly during last decades for its clean and renewable characteristics.The global cumulative installed wind capacity has already exceed 486.7GW,which will continue growing in the following decades.Driven by the requirements in energy capture and wind turbine technology,the scope and size of modern wind turbine have grown considerably and single turbine power can reach a capacity of 8-10 MW with rotor diameters in excess of 160 m.However,various harmful environmental conditions,such as rain drops,windblown sand and dust particles among others could be of great threatens to the mechanical integrity of the wind turbine blade,especially at the leading edge.Leading edge erosion has been stated as a challenge and main issue for manufacturers and operators of wind turbines in many articles and reports.Although the detrimental effects of erosion on wind turbine performance have been investigated in some studies,their quantitative influences have not been thoroughly revealed,especially the flow field contours.Therefore,a thoroughly study on the problem of leading edge erosion must be conducted for a deep understanding of the influence mechanism.The dissertation focuses on the influence of different kinds of leading edge erosion and erosion thicknesses or erosion heights and erosion lengths on the aerodynamic force and power output of the horizontal axis wind turbine.The study can provide some theoretical basis for the management,blade maintanence,safe operation and power generation of the wind industrial manufacturers.The main conclusions and results are as follows:A thorough investigation on the influence of leading edge cavity erosion,pits erosion and delamination on the flow field structures,surface pressure coefficients and aerodynamics of S809 airfoil was conducted,in which different erosion lengths and heights were considered and a lot of influential rules were obtained through the study.Results showed that the value of Cl/Cd remains a constant when the cavity erosion length/thickness ratio is greater than 0.5,and the length/thickness ratio of 0.5 can be considered as the critical value for the leading edge cavity erosion.For the pits erosion,the lift and drag coefficients of the airfoil change little when pits depth is larger than 0.5 mm,also the distance between two erosion pits is greater than 8 times of the pits diameter.Meanwhile,the lift drops sharply if the first 5%c of the airfoil is eroded,so the leading edge should be protected in the practical engineering.The results of path coefficient analysis showed that pits density is the most influential parameter,followed by pits depth.For the leading edge delamination,the delamination length of 1%c has the greatest influence on the flow field and aerodynamics of the airfoil,the aerodynamic coefficients of the airfoil grow gradually with the increase of the delamination length,while decrease with the increase of delamination thickness.Therefore,the delamination length of 1%c can be considered as the key influential erosion length for this kind of leading edge erosion.Some corrections have been conducted to improve the calculation accuracy of the traditional Blade Element Momentum Theory(BEM).Based on the improved BEM and the aerodynamic data of the eroded S809 airfoils obtained with CFD method in the third chapter,the physical mechanism and influence rules of the aerodynamic forces of the NREL Phase ? wind turbine blades with different erosions distributed uniform along the blade were elaborated,in which three kinds of leading edge erosion were investigated,that is cavity erosion,pits erosion and delamination.The change rules of the axial and circumferential factors on the sections of the blade span under different erosion parameters,and also the influence rules on torque coefficients and thrust coefficients,power outputs and thrusts of the wind turbine were obtained.With the dimensional method,three leading edge erosion mathematical models were built for calculate the aerodynamic forces variations under the condition of the wind turbine blades eroded with cavity,pits or delamination uniform along the spanwise.After the models building,the erosion coefficients are calibrated and described in figures,and the power output and thrust variations can easily got by finding the erosion coefficients in figure and put them into the models.Compared the influences of the investigated three kinds of leading edge erosion on the aerodynamics of the wind turbine,results show that leading edge cavity erosion has the most serious performance impact,followed by the leading edge delamination and pits erosion.To explore the influence of local erosion on the aerodynamics of the wind turbine,the blade was divided into 10 regions and set the erosion parameters to each region,and the aerodynamic forces of the wind turbine were calculated with the BEM method.Results showed that the leading edge erosion at the outboard(0.7R~1.0R),midspan(0.4R~0.6R)and inboard(0~0.4R)of the blade can lead the aerodynamic forces drop about 60%,30% and 10% of the whole aerodynamic loss,respectively.Accordingly,the blade was divided in to three regions: inborad(I region),midspan(II region)and outboard(III region),to investigate the local erosion effects.Results showed that the erosion at I region has a relative little influence on the aerodynamics of the wind turbine,while the erosion occurred at II and III regions has nearly equal influences on the aerodynamics of wind turbine under the condition of leading edge delamination and cavity erosion.For the pits erosion,the erosion at the outboard(III region)has the most influence on the aerodynamics of the wind turbine.Comparing the shaft power and thrust of the wind turbine with local erosion at I,II and III regions to the wind turbine with leading edge erosion uniform at the whole blade,the weight factors i? and i(38)of the local erosion of the investigated three kinds of erosion were obtained,and which were calibrated by numerical experiments.The complete delamination,pits erosion and cavity erosion models were built by assigning the weight factors to the models built in the fourth chapter.With the models,the aerodynamic force variations of wind turbine blade eroded with different extents and at different locations can be predicted quickly.To validate its accuracy of the models,the aerodynamics of the wind turbine with non-uniform erosions at the leading edge were calculated.The influence of gust and turbulence on the aerodynamics of wind turbine were analyzed based on the wavelet theory,and results showed that the gust and turbulence can cause fluctuation of the aerodynamic forces,the maximum of the shaft power and thrust are about twice as the minimum values.When compared to the average values,the amplitudes of the shaft power and thrust variations caused by gust are greater than that caused by turbulence.Also,the influence of turbulence on the aerodynamic forces of wind turbine with leading edge eroded nonuniformly at the wind speeds of 7m/s and 10m/s,results showed that fluctuation of the turbulence kinetic energy,coherent turbulence kinetic energy,thrust coefficient,power coefficient increase with the increase of wind speed,and the alternate frequencies of extreme values of the aerodynamic forces increase as well.The amplitude of the power coefficient of the wind turbine blades eroded non-uniform is greater that of the blade eroded uniformly,and the maximum amplitude of the power coefficient can reach 99% for the non-uniform eroded wind turbine.3D flow field structures and aerodynamic forces of wind turbine with different leading erosions were simulated with CFD method with the inflow of uniform wind,shear wind and extreme gust,results showed that the flow separation point moves forward and the flow separation region grows with the increase of leading edge erosion under the condition of uniform wind.The maximum pressure of the suction surface decreases tremendously and the differential pressure of the turbine blade decreases when compared the eroded blades to the smooth blade,which indicates that the leading edge erosion can decrease the aerodynamics of the wind turbine.The torque and thrust of the wind turbine decrease with the increase of erosion extents,and the reduction first increase and then decrease with the increase of wind speed.Under the condition of shear wind,the influence of leading edge erosion on the torque coefficient and thrust coefficient was significant,and the average torque coefficient decrease about 42.54% at the wind speed of 10m/s,and that is 54.19% for the wind turbine blade delaminated of 3mm at the wind speed of 20m/s when compared to the smooth blade.For extreme gust inflow,leading edge erosion has little influence on the thrust coefficient,but has great influence on the torque coefficient of the wind turbine,which decreases with the increase of leading edge erosion.Finally,the calculated results were validated by comparing the results obtained by BEM and CFD methods. |
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